The electronic industry has sustained decades of continual reduction of the dimensional scale of integrated circuit features. At the same time, the dimensional scales of both the transistors in the integrated circuits and the electrical connections to the semiconductor chip have also been reduced. The reduction of the scale of transistors allowed more functionality to be integrated into a single chip. More chip functionality provides for the plethora of functionality found in modern electronic devices such as smartphones that can play music, play videos, capture images and communicate using a variety of wireless protocols.
More functionality also calls for more electrical connections into the semiconductor chip and into a package in which it is contained. A semiconductor is typically provided in a package which is sold to original equipment manufacturer (OEM) customers who mount the package on their printed circuit boards (PCB). Alternatively, semiconductor chips without packages are mounted directly on PCBs. The latter attract attention since it is advantageous in terms of an increase in an electric connection and a decrease in cost.
In order to provide mechanical reinforcement between the semiconductor chip and the substrate on which the chip is placed, an underfill material is usually placed. A liquid epoxy resin composition used for existing underfill comprises an epoxy resin and may include other ingredients such as a silica filler, a silane coupling agent and a fluorinated or silicone defoamer. The liquid epoxy resin composition is cured after the space between the semiconductor chip and the substrate on which the chip is placed is filled with it.
As stated above, semiconductor chips are used in portable electronic gadgets such as smartphones. Such portable electronic gadgets, however, are not always treated as sensitive electronic devices, and it is to be expected that they may be dropped, abused or subjected to mechanical shocks. In addition, they might be used in very bad environmental conditions, such as under hot and humid conditions. Against these backgrounds, as for the liquid epoxy resin composition used for underfill, it is demanded that the cured material thereof has an excellent adhesiveness to the semiconductor chip surface and has an excellent moisture resistance.
In recent years, liquid epoxy resin compositions that have an excellent adhesiveness to semiconductor chip surfaces have been proposed (for instance, see patent documents 1 and 2).